http://www.wizards.com/Magic/Magazine/A ... daily/ld/2
Extended
For many readers, the biggest surprise to come out of the recent announcement was the decision to ban Sensei’s Divining Top in Extended. Making the decision to remove a card from an environment completely is never something taken lightly, and this time was no exception. Sensei's Divining Top caught the eye of Organized Play as being a potential problem during the Qualifier season for Pro Tour–Hollywood, but ultimately the decision was to monitor Top’s performance through the season and reconvene on the matter later in the year.
Sensei's Divining Top
Ultimately Top 8s throughout the season were littered with the one-cost artifact either in conjunction with Counterbalance to lock opponents out of games, Trinket Mage to be found reliably, or (and usually in addition to) Onslaught’s sac-lands to allow players to shuffle away cards they didn’t wish to draw while peeking at a fresh set of three cards. Such a pervasive performance during a single season created a different problem as well: it made tournaments take too much time.
The constant activating of Divining Top bogs games down, which ultimately leads to an increase in the number of matches that go to time and beyond, which in turn leads to tournaments running much longer than they have historically. Furthermore, the Top encourages players to maximize the number of shuffle effects they play in a deck and the constant shuffling, cutting, presenting to an opponent to repeat the process, and then continuation of a turn exacerbated the situation. In the past the DCI has banned such cards on those grounds alone (Shahrazad is a good example of this, with Land Tax and Thawing Glaciers also having been banned for similar reasons) but in conjunction with the Top’s popularity during the last Extended PTQ season, the decision was to ban the card from the format it was harming.